A hermetic terminal has been used which is configured to be fixable to a mounting hole provided in a hermetic container in order to supply a signal or power to an electric device contained in the hermetic container. For example, in a compressor used for an air conditioner, refrigerator, or the like, power is supplied from a power supply to a motor in a container of a motor unit via a hermetic terminal hermetically fixed to the container.
Since a compressor such as that in the air conditioner or refrigerator has a motor therein, electrically conductive particles resulting from wear of a sliding portion such as a bearing are gradually accumulated in refrigerant and refrigerator oil. When these electrically conductive particles are adhered to a surface of a glass insulatively sealing a metal stem and an electrode rod of the hermetic terminal, an insulation resistance between the metal stem and the electrode rod is decreased gradually, which may result in a short circuit in an extreme case.
When such a short circuit occurs between the metal stem and the electrode rod, overcurrent may flow to increase temperature and accordingly melt the sealing glass, with the result that the electrode rod may be removed from the metal stem and the oil in the compressor may leak to outside. In order to prevent such a phenomenon, a hermetic terminal with a fuse region has been conventionally used. The hermetic terminal has a conductive pin provided with a portion that generates heat when supplied with power. When overcurrent flows, the heat generating portion is melted and disconnected, thus interrupting supply of power to the motor.
For example, a hermetic terminal described in Patent Document 1 is provided with a fuse region constituted of a neck portion having a small cross sectional area at an axial intermediate portion of a conductive pin of the hermetic terminal. Since the conductive pin itself has a current fuse function, the fuse region is melted and disconnected when overcurrent is applied thereto, thereby interrupting supply of power. In this way, the motor is prevented from being burned out.
In Patent Document 2, a pin material is roll-formed to provide a fuse region in a conductive pin. By the roll forming, a flange is formed in the pin material, thereby forming a small-diameter groove that defines the fuse region.
However, in each of the conventional hermetic terminals with the fuse regions, a portion of the conductive pin is formed to have a small diameter, thereby forming the fuse region having a small conductive capacity. When overcurrent is applied, this fuse region is heated to be red hot due to resistance heating, is then melted, and is disconnected. Therefore, in each of the conventional hermetic terminals with the fuse regions, it takes a long time until the conductive pin, which is composed of a steel material or copper material, is heated to be red hot and is disconnected due to the overcurrent. Moreover, the melting/disconnection temperature is also high to be more than 1000° C. Moreover, the fuse region of the conductive pin may not be disconnected as intended. Actually, a portion of connection of the conductive pin with an interconnection may be disconnected first. Thus, the disconnection does not always take place at the same portion, disadvantageously.
Further, when it takes a certain time or more for the fuse to be melted and disconnected, the glass serving as the insulating sealing material near the fuse region may be melted first, with the result that the conductive pin may be removed due to refrigerant internal pressure. To address this, in the hermetic terminal of Patent Document 2, the flange is provided in the conductive pin to prevent the removal of the conductive pin.
In the hermetic terminal of Patent Document 3, a high melting point glass material is used for the insulating sealing material. This makes it difficult to melt the insulating sealing material. However, use of such a special high melting point glass material leads to increased material cost. Moreover, an operation temperature in the glass sealing step needs to be changed to a higher temperature. These are not necessarily preferable in terms of product cost and production energy efficiency.